FIG. 1 shows a conventional coupling lock interposed in a coupling device adapted for interconnecting the truck and the container together. The conventional coupling lock comprises a core member 81, a locking member 82, a driving piece 83, a core housing 84, an outer housing 85 and a locking plug 86. The core housing 84 has a slot 841 at the top end thereof and the locking member 82 is received the slot 841 for free sliding. The locking member 82 has a hook portion 821 to engage with an annular slot 861 of the locking plug 86 as shown in FIG. 2, such that the locking plug 86 will be coupled with the core housing 84 and the outer housing 85 fixedly.
The only means to couple the locking plug 86 of the conventional coupling lock is the hook portion 821 of the locking member 82 so that the conventional coupling lock has a weak capacity to couple the truck with the container. If the truck runs on a rough road, the locking member 82 may fail to hook the locking plug 86, such that the container may detach from the truck.